As disclosed e.g. in WO 2012/033178A1, research and development has been conducted on a projection display device which projects image lights formed of lights of different polarization components. Such a projection display device can be used as a device which, in combination with dedicated glasses, displays three-dimensional images by a so-called “passive polarization method” or “polarizing glass method”. In order to project image lights of different polarization components, it is necessary to provide the same number of projectors as the number of the image lights, or to incorporate the same number, as the number of the image lights, of spatial light modulators for forming images and illumination devices for illuminating the special light modulators into one projector. As an alternative, a method is employed which comprises switching polarization components in a time-divisional manner by using a device having a liquid crystal element after emitting image lights from a projector. The conventional projectors and projection display devices thus involve the problem of being large-sized and complicated.
On the other hand, in the projector and the projection display device disclosed in WO 2012/033178A1, a spatial light modulator is illuminated time-divisionally with lights of different polarization components and, in addition, modulated images corresponding to the lights of different polarization components are formed in a time-divisional manner. Such projector and projection display device can display 3D images while achieving a significant reduction in the size of the device.
A projector using a source of coherent light, such as laser light, has the problem of the formation of speckles. The “speckles” refer to a speckle pattern that may appear on a scattering surface when irradiated with coherent light such as laser light and, when formed on a screen, are observed as speckled uneven luminance (uneven brightness) which can have a physiologically harmful influence on the viewer. In the projector and the projection display device disclosed in WO 2012/033178A1, an optical element is irradiated with coherent light in such a manner that the coherent light scans the optical element. This can effectively prevent the formation of speckles on a region when it is illuminated with illumination light from the optical element. The related-art projector and projection display device are favorable also in this regard.